1. Field of The Invention
This invention relates to lasers and laser systems, and, in one aspect to a laser-device for producing a hole in skin through which blood may be withdrawn. In one particular aspect this invention relates to modifying the output profile of a laser beam to produce improved skin perforators.
2. Description or Related Art
Capillary blood sampling is a process for obtaining blood samples from the sub-dermal capillary beds of patients. A common method is to produce a small wound in the patient's skin using a sharp needle or small blade, called a blood lancet. Lancets are commonly used once and discarded. The lancet procedure produces a sharp, blood infected waste product which represents a risk to patients and healthcare workers, and which must be disposed of under carefully controlled conditions. In addition, the use of disposable blood lancets requires the healthcare providing organization to maintain a large inventory of disposable lancets. Certain lancet designs include an exposed point which produce significant fear and apprehension in patients who anticipated a painful experience. Although modern designs have attempted to eliminate such apprehension, reduction of patient discomfort would significantly increase the usefulness of new capillary sampling techniques.
Solid state lasers typically have a light source for optical excitation, an active laser material, and a set of reflecting mirrors. Most solid state lasers have a design with a rod of laser crystal or glass material optically pumped by a high intensity lamp with mirrors placed a distance from, or in contact with, or coated onto, the surfaces of the laser rod. One mirror has either a hole or a reduced reflectance relative to the other. Light is injected from the lamp or LED array into the laser material initiating the discharge of photons from dopants in the rod. These photons travel between the two mirrors producing light amplification. The amplified laser beam escapes the system through the hole or area of reduced reflectance. As an active medium one can use various lasant materials to produce different wavelengths of laser light. These materials include, but are not limited to, rare-earth-doped oxide and fluoride laser crystals and glasses, e.g. yttrium-aluminum-garnet (YAG). Such crystals and glasses will be doped with impurities to fix the resultant wavelength of the laser. These traditional laser designs have precise mirrored surfaces. The reflective surfaces are usually made by coating the surfaces with several thin layers of dielectric material. If separate mirrors are used, they are placed precisely with respect to the optical axis of the laser rod and with respect to each other. The reflective mirror surfaces can be also produced by coating them onto the polished faces of a laser crystal.
Modal distribution is a property of guided light. A projection mode can be characterized by an angular direction vector in which light beams may travel with respect to some normal angle. The normal angle is defined usually as 0 degrees with respect to the optical axis of a system. The modal distribution of a system can be characterized by a set of angular vectors in which light travels upon output from the system. A low order distribution is one in which most of the energy in a light beam travels parallel or near to parallel with the optical axis with a single centroid. Most commonly available laser devices are designed to have a low order distribution of modes; i.e., most devices are preferably designed so that light energy travels only in the TEM.sub..infin. mode (parallel and close to the normal vector with low order distribution) or within a small set of angular vectors surrounding the normal vector. A higher order distribution is one in which energy light travels at greater angles in more complex patterns with respect to the optical axis.
Prior art lasers have been used for cutting materials such as skin tissue. Such laser devices, in general, have four distinct functional stages: 1) pumping, in which the laser gain material is stimulated to produce monochromatic emission; 2) resonation, in which the stimulated emission is amplified and the fundamental radiative properties of the beam are created; 3) output conditioning, in which optical devices such as lenses and filters are used to condition the emitted light into a suitable form for transmission; and 4) delivery, in which the light energy is projected onto the target in a useful manner. Prior art biomedical lasers have one of three delivery methods: 1) contact method, in which a solid transparent light delivery means is placed in direct contact with tissue to be cut or ablated and energy is transferred to the target tissue primarily by conduction; 2) non-contact method, in which the laser beam is projected through a transparent fluid medium, such as air, and energy is transferred primarily by radiation; and 3) indirect method, wherein one of the first two methods is used to heat an additional surface which, in turn, destroys the target tissue though conduction of black-body heat.
Prior art solid-state laser devices typically include various common elements such as: a) a rod of laser gain material composed of a host material (e.g., yttrium aluminum garnet, YAG) and dopant such as Holmium, Erbium, or Neodynium; b) a pumping source which emits photons into the gain material, such as a flashlamp or laser diode; c) a resonating chamber composed of reflective mechanisms which produce a coherent standing wave within the gain material, such as reflective coatings on the ends of the gain material rod or external mirrors mounted parallel to the ends of the gain rod; d) a reflector which may surround the pump source and gain rod and which directs photons toward the gain rod; e) beam conditioning optics which modify the laser output of the resonator and direct such energy toward a delivery mechanism, or towards the work target; and d) a delivery mechanism which collects emitted laser energy and transmits it to the work target. Each of these elements may be composed of various optical components and materials.
The light emitted by most lasers contains several discrete optical frequencies which can be associated with different modes of the optical resonator. It is common practice to categorize two types of resonator modes: transverse modes and temporal modes. The beam characteristics of a laser such as divergence, diameter, and cross-sectional energy distribution are governed primarily by the transverse modes. The modal distribution of a particular laser is a critical factor in determining its suitability for a given application. In general, laser beam quality is regarded as being higher when modal distribution is kept to a low order. This provides significant advantages in energy density and precision for many applications. U.S. Pat. No. 5,352,495 to Henderson et al teaches controlling modal distribution for the treatment of surfaces by a laser. Henderson further teaches achieving higher-order modal distributions by insuring the production of a large number of modes for the purposes of, e.g., marking paper. In an example Henderson introduces the concept of a "top hat" mode distribution, a combination of a plurality of single modes.
A variety of low-order and single mode lasers have been developed and are used in medical applications such as eye surgery, general surgery, tissue necrosis, and sensor probes. Laser skin perforators for capillary blood sampling are disclosed in U.S. Pat. No. 5,165,418, in Japanese Patent 4,314,428, and in PCT patent application U.S. 93/10279. Certain lasers of the type described in these publications will typically exhibit a low order distribution of modes with radiant energy concentrated toward the center of the beam and, thus, the holes, or wounds, produced are relatively deep and penetrating with respect to the thickness of the skin. Such wounds are the shape of a champagne glass with a broad entrance wound and a longer slender stem. The Russian scientific abstract "Non-contact device for blood taking" from the Moscow-Brest conference of 1990 on lasers in medicine specifically discusses this effect. Blood is found to be available from the upper bowl portion of the wound, but little blood escapes from the lower portion, or stem, of the wound.
There has long been a need to produce capillary blood samples without the production of hazardous waste products. There has long been a need to eliminate the use of disposable implements for performing such procedures while reducing worker exposure to infectious disease. There has long been a need to reduce patient discomfort and pain associated with capillary blood collection.